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gangster Jul 26, 2013 06:33 PM
mac pro mem timing
i came across 8gb of fb-dimm ram (2x4gb) that is marked pc2-6400f -800 ecc that i wish to add to my existing 4x2gb ram of the same spec. i see what i believe is a timing spec of 555-11 on my original ram, but nothing on the "new" stuff. should i expect any conflict? also, how do i configure 6 fb-dimms in 2 risers? currently there are 2 in each riser.

thanks in advance.
Waragainstsleep Jul 26, 2013 09:30 PM
In a 2008 quad or 8-core Mac Pro, if you want to use 6 DIMMs, you should have two matched pairs in the top riser and one matched pair in the bottom riser. If you already have a pair in each riser nearest to the logic board, then just put the new pair in the two empty slots on the top riser. I think they are labelled 3 and 4.

I can tell you the 555 is correct. I can't see anything about the 11 part anywhere in my literature.

These are pretty handy things to come across. Usually almost $300.
gangster Jul 26, 2013 11:07 PM
thanks for the quick reply.

i saw some fb-dimms on ebay claiming 666-11 timing so i was concerned but i plan to try the "new" ones tomorrow no matter what.

so i dont need to put the 2 4gb dimms alone together on a riser , i can mix sizes on the same riser as long as they are matched pairs side by side?

thanks again.
Waragainstsleep Jul 27, 2013 07:21 AM
If you split them between risers, I don't think it'll work reliably.

Take a look:

I recently bought some of this type of RAM but mine is going in an Xserve rather than a Pro. Most of the ones I found were expensive but I managed to get 4x1GB and 2x2GB for £50 the lot. Of course, now I have to find some smaller heat spreaders for them....
gangster Jul 27, 2013 10:24 AM
worked like a charm using the diagram!

ghporter Jul 27, 2013 06:16 PM
Great answer to a great question. I'm moving this thread to the Desktops forum where it belongs. That will get more people an opportunity to find it when looking for Mac Pro memory...
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